The object of the invention is a machine for machining a work piece with at least one tool, having a ball screw, which is supported by a fix and a floating bearing.
For precision machining of work pieces, such as for milling, grinding, EDM machines, lathe etc., it is necessary that a table for workpieces is held over a nut on a ball screw and is positioned with a precision equivalent to the desired precision of the outcome of the work. As a rule, the position of the nut of the ballscrew is supported by one or more positioning devices.
The U.S. Pat. No. 6,958,588 B2 discloses a machine for machining a work piece with at least one revolving or rotating tool has a work spindle with a shaft, whose temperature is monitored by means of at least one temperature sensor. The temperature sensor is detected in contact less fashion. The sensor is preferably a radiation-sensitive sensor, which detects the temperature radiation output. In triggering the positioning drive mechanisms, the control unit of the machine takes into account the temperature expansions of the shaft that result from the temperature changes in the shaft. The positioning drive mechanisms serve to position a tool, carried by the shaft, relative to the work piece. A machining precision is thus achieved that is independent of the temperature and temperature changes of the machine overall, of temperature changes in the coolant lubricant, and of temperature changes in the tool and the shaft, that can all be caused by the power converted at the machining site.
In the U.S. Pat. No. 6,456,896B1 another apparatus and a method for thermal displacement correction for a machine tool is described. The position of a feed shaft is monitored, the mean moving speed and moving frequency of the feed shaft arc measured with every unit time for position correction, and a correction amount is determined from the speed and frequency according to an approximation formula and updated. A position correction amount for a commanded position is determined from this correction amount, and the commanded position is corrected by the position correction amount. The position correction amount for the commanded position is determined from this correction amount, and the commanded position is corrected by this position correction amount. Since the correction amount is determined according to the approximation formula, thermal displacement correction can be effected at all times without requiring any sensor. When the correction amount changes substantially, the thermal displacement is measured by means of a sensor and used as the correction amount, whereby accuracy is improved. The frequency of measurement by means of sensors is reduced, so that the machining time can be reduced.
The object of the invention is to provide a device for compensation thermal caused displacement for generating a better accuracy and an improved better utilization of machining time in a simple way without any complexity.